Question

Prove that Sin3A +Sin7A +Sin10A = 4Sin5A time Cos7A/2 time cos3A/2​

Answer 1

Use formula:-

sin3a+sin7a = 2sin5acos2a , and sin10a = 2sin5acos5a

sin3A+sin7A+sin10A = 2sin5a(cos2a + cos5a) = 2sin5a ( 2cos7a/2 cos 3a/2) = 4sin5A cos 7A/2 cos 3A/2

2/

use formula sinx - siny = 2 sin[(x-y)/2]cos[(x+y)/2] and cox+cosy = 2cos[(x+y)/2]cos(x-y)/2]